1. Field of the Invention
The present invention relates to a photoresist ashing residue cleaning agent used after the ashing of the photoresist in the production of a semiconductor circuit pattern.
2. Description of the Prior Art
Elements such as ICs and LSIs on a semiconductor wafer are generally produced by forming fine electronic circuit patterns on a substrate wafer relying upon the photolithography technology. Concretely speaking, a photoresist is applied onto the substrate wafer on which are formed an insulating layer such as an SiO.sub.2 layer and an electrically conducting layer of a metal such as Al, Cu, Si, Ti, etc. or an alloy thereof, which is, then, developed by exposure to light through a mask on which is formed a desired pattern to form a resist pattern on a desired portion. Then, the treatment such as etching is effected for the insulating layer and the electrically conducting layer from the upper side of the resist pattern, and the resist is, then, removed. In forming the semiconductor circuit pattern as described above, the photoresist has heretofore been removed by using a photoresist remove solution comprising various organic solvents.
In recent years, however, there has generally been employed a method of removing the photoresist by the so-called ashing treatment according to which the photoresist is removed by being ashed utilizing the energy of plasma, in order to precisely remove the photoresist after having formed a fine resist pattern, featuring simple operation yet meeting the demand for forming circuit patterns maintaining precision. On the surface from where the photoresist is removed by ashing treatment, however, there remain the incompletely ashed product of photoresist and the side-wall polymer formed in the step of etching without being removed to a sufficient degree through the above-mentioned treatment.
Here, the side-wall polymer is a low solubility product formed on the side walls of the photoresist mask in the step of etching as a result of a complex reaction of an etching gas with the photoresist or with the underlying electrically conducting layer, insulating layer and substrate. The side-wall polymer may often be intentionally formed in order to enhance the effect of anisotropic etching or may be formed unintentionally. When the reactive ion etching (RIE) is conducted, the side-wall polymer and the incompletely ashed product of photoresist may exhibit particularly low solubility. The RIE is a method according to which a negative voltage is applied to the wafer which is a substrate, a reactive gas containing a halogen gas such as of carbon fluoride, hydrogen fluoride or hydrogen chloride is irradiated with a plasma to etch the layer that is to be treated, and has in recent years been chiefly employed as a dry etching featuring excellent anisotropy.
The photoresist to be removed by the ashing treatment may be degenerated when it is exposed to the ion-implantation treatment. After the ashing treatment, therefore, the incompletely ashed product of photoresist is formed to a conspicuous degree. The ion-implantation treatment is the operation for implanting ions of phosphorus, boron, arsenic, indium, antimony or titanium in order to form an electrically conducting portion at a desired place in the insulating substrate wafer while masking the surface thereof with a resist pattern.
The incompletely ashed product of photoresist and the side-wall polymer (hereinafter they are referred to as photoresist ashing residue or simply ashing residue) remaining on the surface from where they are removed after the ashing treatment, could cause defective contact to the interconnection and must, hence, be removed by washing. Therefore, the solution comprising various organic solvents such as those used as the above-mentioned photoresist remove solution, has been used as a cleaning agent to remove the residue. In fact, however, the photoresist ashing residue has been polymerized to a high degree and is becoming inorganic to a considerable degree, and dissolves little in an organic solvent, and cannot be removed with these cleaning agents to a sufficient degree.
Under such circumstances, Japanese Unexamined Patent Publication (Kokai) No. 197681/1997 discloses a composition comprising a fluoride such as ammonium fluoride, a water-soluble organic solvent and water as a cleaning agent for the above-mentioned photoresist ashing residue. Owing to the action of the fluoride and water, this composition is capable of dissolving and removing the ashing residue considerably favorably. It is, however, demanded to further enhance the dissolving power to dissolve the residue having low solubility, such as the side-wall polymer formed by the RIE and the incompletely ashed product of photoresist degenerated by the ion-implanting treatment. However, when the amount of use of the organic solvent is decreased to render it to be highly inorganic such that the cleaning agent exhibits further enhanced dissolving power for the photoresist ashing residue, the underlying electrically conducting layer and insulating layer may be corroded by the cleaning treatment causing a serious problem.
It has therefore been desired to develop a photoresist ashing residue cleaning agent capable of favorably removing the photoresist ashing residue such as incompletely ashed product of photoresist and side-wall polymer, causing the insulating layer and the electrically conducing layer on the substrate wafer to be little corroded.